The Watson-Crick structure is the B form DNA, or B-DNA that is the most stable structure for a random-sequence DNA molecule under physiological conditions. The DNA is arranged in a right-handed double helix, but the helix is 20˚A wider and the number of base pairs per helical turn is around 10.5. The plane of the base pairs in B-DNA is tilted about 6 degree with respect to the helix axis. Correct answer is D.